Have you tried -webkit-hyphens on the actual device? Because it does work in Kindle Previewer, and I would hope that they used the same version of GTK WebKit....

KindlePreviewer is utterly unreliable. It often shows support for formatting not available on the actual devices and vice versa.

On eInk Kindles soft-hyphens work, but automatic hyphenation does not work no matter what hypenation style you use. You may want to test Kindle books on actual devices or the Kindle for PC app before making blanket statements.

Because it does work in Kindle Previewer, and I would hope that they used the same version of GTK WebKit....

You know what they say: hope in one hand... crap in the other... see which one fills up first.

I may be wrong about the Kindle for iPhone app. It may not support auto-hyphenation at all. I don't have a device to test it on.

For that matter, I'm not even really convinced that the Kindle Fire's (or any of the other eInk devices') KF8 reader/renderer is based on WebKit. The Silk Browser is definitely based on WebKit, though.

On eInk Kindles soft-hyphens work, but automatic hyphenation does not work no matter what hypenation style you use. You may want to test Kindle books on actual devices or the Kindle for PC app before making blanket statements.

I didn't make any blanket statements, first, and second, I noted that it does not work in Paperwhite (eInk) previewer mode (unless I deleted that part in editing). I'm not sure why you thought I was talking about those.

[Edit: looks like I deleted my snarky cheap shot at Kindle Paperwhite preview mode's bugfest in editing. So I just said that it worked in Fire and Fire HD previewer modes, and left the rest to implication. ]

I just wanted to add a couple of points. Don't trust the Kindle Previewer. It usually works ok for the Kindle Fire modes, but all of the rest of the modes are broken in various ways.

The KF8 HTML/CSS renderer is based on the Webkit browser. That's a fact. There are lots of features that are undocumented by Amazon, but work just fine. In my production process, I prefer to run the book's text through a hyphenation algorithm and insert soft hyphens (which doesn't require jailbreaking, it will work on any KF8 capable Kindle), but it doesn't surprise me that -webkit CSS feature works.

I just wanted to add a couple of points. Don't trust the Kindle Previewer. It usually works ok for the Kindle Fire modes, but all of the rest of the modes are broken in various ways.

The KF8 HTML/CSS renderer is based on the Webkit browser. That's a fact. There are lots of features that are undocumented by Amazon, but work just fine. In my production process, I prefer to run the book's text through a hyphenation algorithm and insert soft hyphens (which doesn't require jailbreaking, it will work on any KF8 capable Kindle), but it doesn't surprise me that -webkit CSS feature works.

Please, don't add the soft hyphens if you are planning on selling these eBooks. All it is going to do is bloat the size of the KF8 and possibly screw up the Mobi. Most people won't be bothered by not having the soft hyphens. And given that the PW has less memory then previous models, it's just wasting that memory to have the soft hyphens.

Of course, if they are for your own personal use, that's fine for you to do whatever it is that you like.

Please, don't add the soft hyphens if you are planning on selling these eBooks. All it is going to do is bloat the size of the KF8 and possibly screw up the Mobi. Most people won't be bothered by not having the soft hyphens. And given that the PW has less memory then previous models, it's just wasting that memory to have the soft hyphens.

Of course, if they are for your own personal use, that's fine for you to do whatever it is that you like.

Bloat? Really? Have you measured the increased file size? What no one will notice is the increased file size. As for the difference in the appearance, it is a striking improvement, especially for folks who like to use a larger font size. Those huge rivers of whitespace running through Kindle books may not bother you young folks, but plenty of older folks need this.

And, Kindlegen has been removing the soft hyphens from the old .mobi format since version 2.4. But, I test my books just to be sure.